Food safety is an important public health issue. One aspect of food safety is insuring that residue concentrations of drugs and other compounds in consumable products derived from food animals are at, or below, levels that are acceptable for human consumption. Programs for insuring such requirements are met are administered by various government regulatory agencies such as (in the United States) the Food and Drug Administration (FDA) and the United States Department of Agriculture (USDA).
In general, veterinary pharmaceutical products must meet standards of safety and efficacy, in much the same manner as human pharmaceutical products. In addition, it must be assured that an adequate time elapses between treatment of an animal and the harvesting of consumable products from that animal. Such times are termed "withdrawal times". From factors such as an acceptable daily intake of a given compound for human consumption, certain assumptions on the composition of the diet of a given population, maximum residual levels (MRL; referred to as tolerance level in the United States) for various compounds in food products are determined. The withdrawal time is an indication of the time required, after treatment by or exposure to a particular compound, for the concentration of a compound (or byproduct of that compound) to reduce to a level at or below the tolerance in the tissue of interest (e.g., milk, meat). Once the withdrawal interval has elapsed, the tissue of interest can be harvested and used for human consumption. Food products are monitored for compliance with such tolerances, and the detection of levels in excess of acceptable tolerances can result in legal penalties.
Withdrawal intervals are currently determined empirically: a group of animals is administered a known drug at the dosage for which approval is sought, and animals within that group are sacrificed over time and the amount of the drug or residue measured in the tissue of interest. The withdrawal time is determined from the pharmacological data so obtained. A problem with this approach is that such studies require utilization of large groups of animals. An additional problem is that the study must be repeated, with an additional group of animals, when a new dosage is contemplated.
Veterinary and humane considerations can weigh in favor of using an approved drug for a sick animal at a dosage for which a withdrawal time is not known. In cases like this, either a best guess of a withdrawal time must be made, or an animal study must be conducted. If an insufficient withdrawal time is used and unacceptably high levels of the drug are detected in tissue derived from the treated animal, then legal liability under applicable food safety statutes may nevertheless attach.
Accordingly, there is a need for new techniques for determining withdrawal intervals in food animals.